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Technical Overview
Before we examine the tariff provisions involved and get into the inner workings of the tariff classification process, a brief primer on engine technology would be helpful.
Most sources commonly define an engine as a machine or apparatus for converting energy into mechanical power or motion. The engine\'s purpose is to translate the potential energy locked in a fuel into a rotating force called \"torque\", which is a twisting force or action that performs work. It is created in the engine by burning a mixture of fuel and air at a controlled rate. This is called combustion and when it occurs within the confines of an enclosed cylinder, it is referred to as internal combustion, as opposed to engines, which burn their fuel externally like the steam engine of an old-fashioned paddle wheeler that employs steam raised in a fire-driven boiler to drive a piston up and down in a cylinder.
Internal combustion engines, then, for the purposes of this discussion, are those in which power is produced by burning fuel inside a combustion chamber or cylinder containing a piston which goes up and down in a reciprocating motion resulting from the combustion. Extending down from the piston is a connecting rod, which links the piston to the crankshaft. The connecting rod and crankshaft convert the reciprocating motion of the piston into motion or work.
Technically, internal combustion engines can be categorized in many ways. The most common ways of talking about engines include the combustion cycle, the valve location, the cooling system, the number and placement of the cylinders and the type of fuel used.
Most internal combustion engines use a two- or four-stroke combustion cycle. The vast majority of automobile engines are of the four-stroke cycle type. In this type, there is an intake stroke, wherein the intake valve opens to admit the air/fuel mixture to be burned during one complete cycle. Next is the compression stroke, wherein the mixture is squeezed into a smaller volume than as admitted. The power stroke, which comes next, ignites the mixture, which forcefully thrusts the piston into turning the crankshaft, whose power is then transmitted into motion or work. Finally, the exhaust stroke results in the opening of the exhaust valve to vent the spent gases of the power stroke. The rotary engine, or Wankel engine (named after its inventor), also uses a four-stroke cycle, but does not employ conventional pistons. Instead it uses triangular rotors which function like pistons, but in place of the up and down reciprocating motion of the piston, the rotors continually revolve in the same direction as their eccentric shafts.
The two-stroke cycle engine reduces these strokes from four to two and does not employ valves. Two-stroke engines can operate at very high speeds and can be compact and light. Thus, they are popular in small engine operations such as chain saws, lawn mowers, marine outboard motors and the like. They are not noted for fuel efficiency or emissions control.
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